1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method which are of an electrophotographic type, an electrostatic recording type, or the like.
2. Description of the Related Art
There has conventionally been proposed a one drum type multicolor image forming apparatus capable of forming a color image. This image forming apparatus irradiates a drum-shaped electrophotographic photosensitive member as an image carrier, i.e., a photosensitive drum with laser beams or light from a light-emitting element such as an LED and forms electrostatic latent images on the photosensitive drum by an electrophotographic process. The electrostatic latent images are converted into visible images (toner images) for respective color components such as magenta (M), cyan (C), yellow (Y), and black (BK) using developing agents (toners) of the respective color components. In a transfer section, the toner images on the photosensitive drum are multiply transferred onto a transfer material conveyed by a drum-shaped transfer material conveying member (transfer drum) or the images are multiply transferred onto a belt-shaped intermediate transfer member (intermediate transfer belt) and then collectively transferred onto the transfer material.
There has also conventionally been proposed a color image forming apparatus having a plurality of photosensitive drums. This image forming apparatus includes a plurality of image forming sections, each of which performs a latent image forming step and a image development step on a corresponding photosensitive drum by an electrophotographic process. In a transfer section, toner images obtained in the image development step are multiply transferred onto a transfer material conveyed by a belt-shaped transfer material conveying member (transfer conveying belt) or the images are multiply transferred onto a belt-shaped intermediate transfer member (intermediate transfer belt) and then collectively transferred onto the transfer material.
An image forming apparatus of this type may suffer so-called “color misregistration” that is, a phenomenon in which images of respective colors are out of alignment when they are finally multiply transferred onto a transfer material. In particular, in a color image forming apparatus having a plurality of photosensitive drums, “color misregistration” may occur due to mechanical mounting errors among the photosensitive drums, errors in optical path length among laser beams, a change in optical path, or the like.
To cope with this, there is known an image forming apparatus which corrects color misregistration (see, e.g., Japanese Patent No. 02603254). In this image forming apparatus, optical sensors arranged adjacent to a photosensitive drum of an image forming section on the lowermost stream side read color misregistration correcting patterns formed on an intermediate transfer member (transfer and conveying belt) and detect color misregistration among images of respective colors formed on the transfer and conveying belt by image forming sections. The image forming apparatus performs electrical correction for image signals to be recorded on the basis of the detected color misregistration and, additionally or alternatively, drives turn-back mirrors provided in a laser beam optical path to automatically correct errors in optical path length or a change in optical path (a mode of performing automatic correction will hereinafter be referred to as an automatic adjustment mode).
The automatic adjustment mode is automatically activated, e.g., on the basis of the number of images formed or the number of hours the machine is used or at power-on to automatically correct process conditions for image formation.
Since a color misregistration correcting pattern is formed a plurality of times in the automatic adjustment mode to reduce errors caused by, e.g., eccentricity in a drive system, the automatic adjustment mode may last for several minutes. Also, the adjustments described above are performed between handling of one paper sheet (recording sheet) and that of another, and once the automatic adjustment mode is activated, image formation cannot be performed until the automatic adjustment mode exits. This reduces productivity.
To cope with this, there is known a technique for sensing color misregistration on the basis of an image formed on a recording sheet and correcting an image writing time and the like on the basis of the image (see, e.g., Japanese Laid-Open Patent Publication (Kokai) No. 9-314911).
However, the technique of Japanese Laid-Open Patent Publication (Kokai) No. 9-314911 suffers the following problems. First, an image with color misregistration is formed on a recording sheet until correction is performed. Secondly, if an appropriate image as shown in the embodiments of Japanese Patent No. 02603254 is not input, it is impossible to accurately perform color misregistration correction.